Chlorine-free refrigerants are desirable for use in refrigerant systems, because their escape into the atmosphere causes less damage to the environment than most commonly used chlorofluorocarbon-based refrigerants (CFC) and hydrochlorofluorocarbon-based refrigerants (HCFC). CFCs are stable, of low toxicity and non-flammable providing low hazard working conditions when used in refrigeration and air conditioning systems. When released, they permeate into the stratosphere and attack the ozone layer which protects the environment from damaging effects of ultraviolet rays.
R-22 is a chemical fluid and by far the largest HCFC refrigerant used globally in refrigeration and air conditioning equipment. R-22 is the subject of a phase-out schedule and any replacement refrigerants cannot deplete the ozone layer. The availability of R-22 will likely be a problem after the HCFC phase-out, and existing equipment using R-22 will need to be retrofitted to a new refrigerant. In normal situations, the compressor must be removed to drain the existing the oil when retrofitting which is a time consuming and costly procedure. Thus, there is a need in the refrigeration and air conditioning industry to provide a refrigerant replacement where replacing the existing oil in the compressor is unnecessary when retrofitting from R-22.
Mineral oils and alkylbenzenes have been conventionally used as lubricants in CFC and HCFC refrigeration systems. However, the lack of solubility of these lubricants in the replacement, non-ozone depleting, hydrofluorocarbon (HFC) refrigerants has precluded their use and necessitated development and use of alternative lubricants for HFC refrigeration systems. Additionally, mineral oils and alkylbenzenes have the desirable feature of being less hygroscopic than the lubricants used with HFCs, and have low solubility, less than 100 ppm, for water. Thus, there is a need and an opportunity to resolve this low HFC refrigerant solubility problem so that the refrigeration industry may utilize mineral oil and alkylbenzene lubricants with HFC-based refrigerants.
HFC refrigerants are replacing CFCs and HCFCs. As detailed above, HFC-based refrigerant mixtures are less soluble than CFCs or HCFCs in conventional refrigeration lubricants such as mineral oils and alkylbenzenes. A lubricant change from mineral oil or alkylbenzene to polyolester lubricants is often required when HFC or HFC mixtures are used to replace pure CFC or HCFC-based refrigerants, resulting in more expense to the refrigeration industry. Thus, there is a need and opportunity to resolve this low solubility problem so that the refrigeration industry may utilize HFC-based refrigerants with mineral oil or alkylbenzene lubricants without having to switch to polyolester lubricants.
In normal hermetic, semi-hermetic or open-drive compressors operating under normal conditions, the compressor pumps oil, such as mineral oil, into the system, condensor side to be specific, holding the refrigerant (air conditioner, refrigerator, etc.). Any amount of oil that is not miscible in the refrigerant composition accumulates in the system and does not readily return to the compressor. This leads to lower amounts of oil return to the compressor, and low levels of lubricating oil in the compressor. A cycle is created of decreased oil return followed by a decreased amount of oil in the compressor and less oil pumped from the compressor into the system. Thus, there is a need and opportunity to resolve this cycle of decreased amount of oil return from the system to the compressor and decreased amount of oil in the compressor.
Traditional methods to improve oil circulation with HFC refrigerants involves the use of solvents that reduce the viscosity of the oil allowing the oil to return from the system more readily. These solvents have high solubility in the oil promoting greatly reduced oil viscosity in the colder parts of the system. These solvents do not promote enhanced solubility of the oil in the liquid refrigerant, and may lead to miscibility problems in the system. There is a need to both simultaneously improve the oil circulation while enhancing the miscibility of the oil in the liquid HFC refrigerant. Known in the art are bridge solvents or compatabilizer solvents which are added to oils to enhance the miscibility thereof. Bridge solvent is a trade terminology for an agent which brings together two phases of a mixture which would not normally come together to form a homogeneous mixture. Examples are oxygenated solvents, such as acetone, which have relatively low boiling points. Additionally, adding the bridge solvents or compatabilizer solvents to the oils directly is difficult because the system is sealed, or leads to problems because of excessive viscosity reduction of the oil in the compressor and potential refrigerant or oil flammability problems. Thus, there is a need and opportunity to provide a method for enhancing the solubility of oils in refrigerant compositions by providing an oil solubility enhancer directly to the refrigerant composition to avoid problems associated with viscosity reducers, bridge solvents or compatabilizer solvents. An additional benefit of the bridge solvents is their higher polarity which leads to a preferential affinity for the metal walls of the tubes in the system. This promotes removal of mineral oil residues from the walls of the system and acts as a cleaning agent.
There is also a need and opportunity to enable the addition of an agent directly to an HFC refrigerant followed by charging the agent/HFC refrigerant mixture directly into the system (air conditioner, refrigerator, etc.) through the system charge ports.